1. Field of the Invention
The present invention relates to a semiconductor pressure-detecting apparatus and, more particularly, to a semiconductor pressure-detecting apparatus for measuring the pressure of a high pressure medium and having a reduced size and cost.
2. Description of the Related Art
FIG. 3 is a cross sectional view which illustrates a conventional semiconductor pressure-detecting apparatus, for example, a pressure sensor. Referring to the drawing, a semiconductor chip 5 has, on the surface thereof, a diaphragm 3 for converting the pressure of oil or the like into stress, the oil or the like being a medium (pressure medium) the pressure of which must be measured. Furthermore, the semiconductor chip 5 has a strain gauge 4 for converting the stress of the diaphragm 3 into an electric signal. The semiconductor chip 5 is placed on a frame 7 for absorbing external stress applied to the semiconductor chip 5, the frame 7 being supported by a metal stem 8. The electric signal converted from the stress of the diaphragm 3 by the strain gauge 4 is taken by a lead 9 via a wire 10 electrically connected to the semiconductor chip 5. The above-described lead 9 is hermetically secured to the stem 8 by glass 11. The semiconductor chip 5 is covered with a cap 13 coupled to the stem 8 so that a reference pressure chamber 6, for example, vacuum, is formed. A case 2 in which the medium 1 to be measured is enclosed is connected to a pipe 14 disposed at the central portion of the stem 8.
The conventional semiconductor pressure-detecting apparatus is constituted as described above so that the pressure of the medium 1 to be measured is applied to the diaphragm 3 via the pipe 14. The diaphragm 3 is distorted in accordance with the difference between the pressure of the medium 1 to be measured and that of the reference pressure chamber 6 so that a resistance change takes place in the strain gauge 4. The resistance change can be converted to a voltage change by means of a structure, for example, four strain gauges 4 connected in a Wheatstone bridge circuit. The voltage applied to the strain gauge 4 or the voltage change due to the resistance change in the strain gauge 4 is given from outside or taken via the wire 10 and the lead 9.
In a case where the medium 1 to be measured is a liquid such as oil, a semiconductor pressure-detecting apparatus of the type described above encounters a problem in that the liquid medium cannot be enclosed adjacent to, i.e., immediately below the diaphragm 3. Furthermore, a pipe 14 must be provided for the stem 8 for the purpose of introducing the medium 1 to be measured. What is even worse, a substrate or the like must be provided for the purpose of supporting the lead 9 since the lead 9 for transferring the electric signal is disposed on the same side on which the pipe 14 and the stem 8 are positioned. In consequence, the size of the apparatus cannot be reduced. Furthermore, if the medium 1 to be measured has a high pressure, the pipe 14 must be welded to the case 2, a very difficult task.